1. Food
&
Digestion

2. Carbohydrates Carbohydrates include sugars and starch
Used in respiration to produce energy
Marathon runners often eat pasta the evening before a race
Too much sugar leads to tooth decay, obesity and sometimes diabetes

3. Testing for Starch
Grind up a little food with a little water using a mortar and pestle to produce a slurry.
Add 2 drops of iodine to a spotting tile
Add 2 drops of the slurry to the iodine
A blue-black colour shows that starch is present
There is not need to heat the mixture!
= starch present = starch absent

4. Testing for Sugars
Grind up a little food with a little water using a mortar and pestle to produce a slurry.
Transfer to a test tube to about 1cm depth
Add 5 drops of Benedict’s solution to the tube
Heat gently in a water bath (beaker of water)
= sugar present

5. Proteins Used for growth and repair
Only used in respiration to during periods of starvation
Body builders have a high protein
Protein is also needed to produce antibodies which help us to fight disease

6. Testing for Proteins
Grind up a little food with a little water using a mortar and pestle to produce a slurry.
Transfer to a test tube to about 1cm depth
Add 5 drops of copper sulphate solution and 5 drops of sodium hydroxide
Do not heat!
= protein present
The stronger the purple colouration, the more protein present.

7. Fats Fats contain more energy than carbohydrates and proteins
Good fats
Fats
Bad fats
Fats contain more energy than carbohydrates and proteins
They are harder to digest and best not eaten before a marathon!
Eating large amounts of fat can lead to obesity and heart disease
Polyunsaturated fats are much healthier than saturated fats
Unsaturated Fats can be trans fat or cis fat. Trans fats are rarely found in naturally growing food other than small amounts in cattle and sheep. Today the largest amount of trans fat consumed is created by the processed food industry. Trans fats greatly increase the risk of heart disease.

8. Testing for Fats There are several methods to test for fat.
For method 1 smear the food over grease proof paper (or tracing paper). Then shine a light through it (hold up to the window). If it looks translucent, fat is present (spot test)
For method 2 grind up a little food with 2 cm3 ethanol (which dissolves fat) and then transfer the clear liquid to a test tube to 1cm depth. Take a second tube and add water to 1 cm depth. Mix the contents of the two tubes. The cloudier the resulting mixture, the greater the amount of fat. The fat forms droplets of fat in water/ethanol mixture known as an emulsion. This is sometimes therefore called the emulsion test.

9. Summary

10. Vitamins
Vitamins are substances needed in very small amounts. They cannot be made by the human body (except vitamin D), so they need to be eaten in our diet. Some are water soluble and often found in fruit and vegetables. Some are fat soluble and found in vegetable oils and oily fish.

11. Vitamins RDA = Recommended Daily Allowance Vitamin RDA Function
Sources
Deficiency A
3mg
Normal growth
Retinal cells
Liver
Carrots
Night blindness B1
1mg
Carbohydrate metabolism
Muscle tone
Whole grain cereals
Beriberi C
90mg
Structure of bones
Helps to maintain gums
Immune system
Citrus fruits
Cabbage
Peppers
Scurvy D
5µg
Structure of bone
Calcium absorption
Egg yolk
Sea fish
Rickets
RDA = Recommended Daily Allowance

12. Deficiency Diseases VITAMIN A Night blindness
Poor vision in low light.
VITAMIN B1
Beriberi
Poor muscle function
Paralysis
Death
VITAMIN C
Scurvy
Bleeding gums
Skin lesions
VITAMIN D
Rickets
Weak bones in growing children

13. Gowland Hopkins Experiment
2 groups of young rats
group A were fed on a diet of purified casein, starch, glucose, lard, minerals and water
Group B were fed the same diet but with the addition of milk
On day 18 the diets were switched.
Group B
Group A
without milk
With milk
For the first 18 days, which was the test group and which was the control?
Why were several rats used in each group?
Why do you think he switched the diets after 18 days?
What conclusions do you think could be drawn from this experiment?
Hopkins' experiments transformed nutrition into a clearly recognized branch of biochemistry founded upon scientific principles. The ability to synthesize products in the laboratory that were identical in properties and physiological effect with the natural vitamins spawned a new industry of nutritional supplements.

14. Vitamin C pre-lab _________ =
DCPIP is used to detect the presence of vitamin C. It is dark blue but changes colour in the presence of vitamin C. We are going to make an estimate of the amount of vitamin C in a fruit juice by comparing its ability to change the colour of DCPIP compared to a known concentration of ascorbic acid (Vitamin C)
Measure out 1 cm3 of DCPIP into a pipette using a pipette filler
Transfer the DCPIP into a test tube
Add the 10mg/100cm3 ascorbic acid to the DCPIP drop by drop using a dropper. Carefully count the number of drops that you use.
Repeat the procedure using the fruit juice.
If time allows, carry out repeated trials
Record your results in a suitably designed table and calculate the mean number of drops.
_________ =
The amount of vitamin C in the fruit juice
Number of drops of ascorbic acid
X 10mg/100cm3
Number of drops of fruit juice

15. = Substance Number of drops Ascorbic acid 20mg/100ml 24 Orange 16
Apple 20
The amount of vitamin C in the fruit juice
Number of drops of ascorbic acid =
Number of drops of fruit juice
X 20mg/100cm3

16. Which colour bell peppers contains the most vitamin C?
Mr Hennie has been suffering from a cold. He is aware that Vitamin C helps to fight off colds and that bell peppers contain large amounts of vitamin C. He wants to include some freshly sliced bell peppers with his salad for lunch, but which colour should he buy?
A slurry can be made by grinding a piece of pepper with water using a mortar and pestle.
The slurry can be tested for vitamin C using DCPIP.
The more drops required, the less vitamin C there is.
Think how the test is to be standardised to ensure a fair test.
How do you obtain results that are reliable and you can trust?
Can you determine the amount of vitamin C?
How can you present the data in a graph?

17. The Digestive System
Draw the diagram in the left half of an A4 piece of paper in landscape. The mouth area can be simplified. Do not copy the writing below.
The liver produces bile which helps in fat digestion. Therefore it is usually included as part of the digestive system
The pancreas produces digestive enzymes.
Duodenum + Ileum = Small intestine
Colon = Large intestine

18. 11
Write out the information to the left in the correct sequence, approximately in line with the relevant structures on your drawing of the digestive system. 2 7 9 3 1 5 10 8 12 4 6

19. Digestion

20. Learning objectives Explain why food needs to be digested
State the role of enzymes in digestion
Identify the types of enzymes that digest food
Explain the importance of villi and microvilli in creating a large surface area in the intestines

21. Chemical Digestion Small, soluble molecules.
Salivary amylase
Simple sugars
Pancreatic amylase
Starch
Amino acids
Proteases
e.g. Pepsin + Trypsin
Protein
Fatty acids and glycerol
Bile salts
Fat/lipid
Lipase
Small, soluble molecules.
These can be absorbed into the blood.
Large, insoluble molecules.

22. Chemical Digestion Small, _______ molecules.
Simple sugars
Starch
Proteases
e.g. Pepsin + Trypsin
Protein
Fatty acids and glycerol
Bile salts
Lipase
Small, _______ molecules.
These can be absorbed into the blood.
______, insoluble molecules.

23. Absorption
Microvilli increase the surface area for absorption

24. Summary
Food substance
Enzyme
End product
Where transported?

25. Investigating the action of pepsin on egg-white suspension
Label your tubes ABCD and initial.
Set up the experiment as shown.
Place in a water bath at 37°C.
Draw and the apparatus using a pencil and ruler.
After 10 minutes, collect your tubes and write down your observations. A
4cm3 egg white
2cm3 pepsin B
4cm3 egg white
6 drops 0.1M
hydrochloric acid C
4cm3 egg white
2cm3 pepsin
6 drops 0.1M
hydrochloric acid D
4cm3 Egg white
2cm3 boiled pepsin
6 drops 0.1M
hydrochloric acid

26. Year 8 Digestion of Starch Practical

27. Digestion of Starch using Amylase
Iodine turns black
Iodine stays brown
Learning objective: To determine the effect of temperature on the digestion of starch

28. Digestion of Starch using Amylase
Four groups
Groups 1 & 3 at room temperature
Groups 2 & 4 at body temperature
Starch turns iodine black!
2 drops of iodine
Groups
2 and 4
Groups
1 and 3
5ml starch suspension
0.5ml amylase
Placed in hand
5ml starch suspension
0.5ml amylase
Placed in beaker

29. Results Time Colour of iodine at room temperature (beaker)
Colour of iodine at body temperature (hand) 1
Black 2 3 4 5 6
Brown 7 8 9 10 11 12